1. Field of the Invention
The present invention relates to an image display apparatus for displaying an image formed by scanning a beam from a light source and, more particularly, to an image display apparatus suitable for scanning a beam by driving a reflecting surface using mechanical resonance.
2. Related Background Art
Various proposals including U.S. Pat. Nos. 5,355,181, 5,369,415, and 5,467,104, and Japanese Patent No. 2,874,208 have been made as an image display optical system (or image display apparatus) for forming an image on the observer""s eye (retina) by scanning a beam from a light source.
FIG. 9 shows the arrangement of an image display optical system disclosed in U.S. Pat. No. 5,355,181. In this image display optical system, a beam from a light source 300 is modulated by an optical modulator 301, enters horizontal and vertical optical deflectors 304 and 305 via optical systems 302 and 303, and reaches an eye 310 via an eyepiece optical system 306 which constitutes a telescope system. The optical deflectors 304 and 305 deflect light incident on the eye 310 and scan an image formed on the retina. This allows the observer to observe a two-dimensional image.
FIG. 10 shows the arrangement of an image display optical system disclosed in U.S. Pat. No. 5,369,415. In this image display optical system, a two-dimensionally scanned beam from a light source 401 scans an eye (retina) 410 via a planar optical system 402. The beam to be scanned is sequentially reflected at a plurality of planar reflecting points within the planar optical system 402, and its optical path is changed toward the eye by a diffraction optical system 403. With this arrangement, the diffracted beam directly scans the retina 410 to enable observing an image.
FIG. 11 shows the arrangement of an image display optical system disclosed in U.S. Pat. No. 5,467,104. In this image display optical system, red, green, and blue light sources 501, 502, and 503 are modulated by light source drivers 504, 505, and 506, and beams from these light sources are combined by a color combining means 507. The combined beam from the light sources passes through the pupil of an eye 510 via an optical system interposed between the color combining means 507 and the eye 510, and is guided on the retina. Vertical and horizontal scanning means 508 and 509 are arranged between the eye and the light sources via an optical system, and scan the beam on the retina.
FIGS. 12A and 12B show the arrangement of an image display optical system disclosed in Japanese Patent No. 2,874,208. As shown in FIG. 12B, a beam from a light source is deflected by a deflection means 602 comprising a polygon mirror, and enters an eye 610 via optical systems 601b and 601c. FIG. 12A shows an arrangement on the optical path from the light source to the eye. Beams from light sources 603, 604, and 605 driven by a data processing and drive signal 620 enter an optical fiber 618 via collimator lenses 606, color combining systems 607, and a lens 609. After passing through the optical fiber 618, the beam further passes through a wavefront curvature modulator 630 and beam deflector 640 via a lens 619, and reaches the eye 610.
These conventional image display optical systems display a two-dimensional image to the observer by forming light from a light source into an image on the retina serving as an image plane and scanning the image point by a scanning means inserted in the optical path.
An apparatus for displaying a two-dimensional image to the observer is, e.g., a liquid crystal panel which enlarges and displays a two-dimensional image as a virtual image via an optical system. To display a finer image, this arrangement requires a larger number of pixels of the image display element. However, a small-size image display element with many pixels is high in cost, increasing the cost of the whole apparatus.
Of the scanning image display apparatuses described above, those disclosed in U.S. Pat. Nos. 5,355,181 and 5,467,104 and Japanese Patent No. 2,874,208 use many lenses, which readily makes the optical system or apparatus bulky.
The image display apparatus disclosed in U.S. Pat. No. 5,369,415 has a relatively simpler arrangement using a flat optical system. However, light is diffracted to the observer""s eye by only the diffraction optical element in front of the eye, so aberration may become difficult to correct for high image quality. Thus, the field angle is difficult to increase.
Japanese Patent No. 2,874,208 adopts a polygon mirror as a deflection (scanning) means, and the deflection means and whole apparatus become bulky.
It is an object of the present invention to provide a small-size, low-cost scanning image display apparatus with a simple arrangement that realizes high-speed beam scan.
To achieve the above object, an image display apparatus according to the present invention comprises scanning unit for scanning a beam by driving a reflecting surface for reflecting a beam from the light source part, an optical element having an incident surface which the reflected beam from the scanning unit enters, at least one inner reflecting surface which has a curved surface and reflects the beam coming from the incident surface, and an exit surface from which the beam reflected by the inner reflecting surface emerges, and a reflecting element for reflecting the beam emerging from the optical element and guiding the beam to an observer""s eye.
Since a beam emitted by the light source unit is scanned by the scanning unit, the prevent invention can provide an image display apparatus which can easily increase the scanning speed and is suitable for displaying a fine image.
The use of the optical element with at least one inner reflecting surface enables deflecting the optical path and easily downsizing the apparatus. Since a beam emitted by the optical element is guided to the eyeball via the reflecting element, the degree of freedom for the layout of the optical system can be increased.
For example, the scanning unit and optical element are arranged on the side of the head with respect to the reflecting element positioned in front of the observer""s eye so as to prevent the observer from feeling uncomfortable. The present invention can implement a scanning image display apparatus which can be used comfortably as if the observer wore glasses.
The inner reflecting surface of the optical element is formed into a curved surface. This structure can satisfactorily correct aberrations such as decentering aberration which readily occur owing to an optical layout capable of guiding a beam from the side of the head to the eyeball via the reflecting element in front of the eye. Accordingly, a high-quality image can be displayed.
The scanning unit is a device which utilizes an MEMS (Micro Electro Mechanical System) technique, is manufactured by a semiconductor process, and has a reflecting surface driven by mechanical resonance. The scanning unit itself can be downsized, scanning can be done at a very high speed, and a smaller-size image display apparatus capable of displaying a fine image can be implemented.
If the beam scanning angle of the scanning unit is enlarged by an optical system made up of an optical element and reflecting element, an image larger than the scanning angle of the scanning unit can be observed.